1. Field of the Invention
The invention relates to an electric domestic appliance which includes a main switch for switching a power supply on and off, which exhibits a predetermined turn-on actuation time period during which it must be actuated in order to be shifted from its off-position into its on-position.
Electrical domestic appliances for which the invention can be used are, in particular, free-standing or installable cookers, ovens, hotplates, grill appliances, coffee machines, dishwashers, washing machines, and dryers.
2. Discussion of the Related Art
The expression “main switch” is used within the framework of the disclosure of the invention to stand for any type of device or element by means of which a power supply can be switched on and off. Thus, a “main switch” can be an individual switch or an electric circuit, which exhibits electrical or electronic components and one or more buttons or sensors. The sensors can be contact sensors or sensors which operate free of contact, such as the prior art already shows.
An electrical domestic appliance is known from DE 42 07 772 C2. There is described a main switch for turning a current supply on and off. The main switch exhibits a predetermined turn-on actuation time period. The main switch must at least be actuated in order for it to be shifted from its off-position to its on-position. The document discloses a main switch in the form of an electric circuit, which exhibits a sensor (light sensor) as its operating element, which must be actuated within a predetermined actuation time period in the range between 0.5 sec. and 1.0 sec. in order to shift the main switch from the off-position into the on-position. This movement only takes place, however, if only this one sensor is actuated, but not if further sensors (light sensors) adjacent to it are touched simultaneously or are covered by a cooking pot or a cloth which has been left lying on it, and reflect light as a result. All the sensors are located on a carrier plate beneath a glass ceramic plate, which is translucent for the light from a light source. The glass ceramic plate forms a cooking surface which contains one or more cooking zones. Adjustment of the time period between the start of actuation and the actual shifting of the main switch from the off-position to the on-position can be achieved by means of an electric time delay element, such as a resistor-capacitor series circuit connection with an electrical tapping point in between, or by means of an electrical circuit with a counter which simulates in a digital manner the properties of the resistor-capacitor circuit.
DE 295 21 593 U1 shows a glass-ceramic hob in the form of a heating hob, which exhibits several cooking zones. An actuating device exhibits contact switches or contact-free switches, by means of which the cooking zones can be switched on and off, and various different temperatures or functions can be set and adjusted. The actuating device contains an on-off button as the main switch, which, when switched on, exhibits a time delay in the range of one to five seconds. The intention is that undesirable switching on should be avoided, for example if a damp cloth is wiped over the on-off button for cleaning purposes.
The actuation time period during which the main switch must be touched or pressed or actuated by fingers being brought close to it, in order for it to shift from an off-position to an on-position, is also a child safety measure. With younger children the risk pertains that they might turn the main switch on unobserved by an adult and so switch on the cooking surfaces, cookers, and ovens. This can lead to a user subsequently burning a hand on a hot cooking plate, or could even cause a fire.
The actuation time, i.e. the dwell time required for a finger on a main switch, which is provided in touch-control technology, up to the actual activation of the domestic appliance, is selected nowadays in such a way that it represents a compromise between erroneous operation safeguard and simple rapid operation. In order to avoid the appliance being switched on unintentionally, for example when cleaning and wiping with a washing-up cloth, or by small children, the actuation time period should be as long as possible. However, in order for operation to be as simple and rapid as possible, the dwell time should be as short as possible. For cooking surfaces, an actuation time for the main switch nowadays is typically, for example, about 0.5 sec.
In earlier designs of cooking surfaces, cookers, and ovens, which have a hob or a glass-ceramic cooking surface, the main switch was sometimes arranged in the rear area of the appliance, so that it was difficult for children to reach, so providing an additional child safety measure. Nowadays the arrangement of sensor operating elements for cooking surfaces is for preference in the front part of the cooking surface, because this is ergonomically more favourable. The arrangement of the main switch in the rear area of the glass-ceramic cooking surfaces is difficult from a technical point of view and also with regard to costs, because, for example, an individual PCB, an additional set of wiring, and modifications to the housing are required. With normal ovens which exhibit a touch-control operation, the main switch, or at least its operating element, can frequently only be arranged on a facia panel.
The invention is intended to resolve the problem, by simple means, of minimising the risk of unintentional switching on of domestic appliances and the risks associated with this. In particular, it is intended that danger to children and damage to property due to children playing should be minimised, in that the unintentional operation of domestic appliances, and of cooking surfaces, cookers,and ovens in particular, should be impeded.